Human growth hormone (hGH) is a protein secreted by the pituitary gland and which can be produced by recombinant genetic engineering. hGH will cause growth in all bodily tissues which are capable of growth.
hGH is typically used to treat patients suffering from hypopituitary dwarfism. Currently, aqueous hGH is administered as a subcutaneous bolus three times a week or once daily to patients to maintain suitable serum levels of hGH. For patients chronically receiving hGH, the frequent injections result in patient compliance problems.
To resolve the problems associated with repetitive injections of aqueous hGH, attempts have been made to formulate controlled release devices containing higher doses of hGH than a bolus injection, encapsulated within a polymeric matrix wherein the hGH would be released in vivo over a period of about a week or more.
However, these controlled release devices often exhibited high initial bursts of hGH release and minimal hGH release thereafter. Further, due to the high concentration of hGH within these controlled release devices, the hGH molecules have tended to aggregate after several days to form aggregated hGH which is immunogenic in vivo and likely has reduced biological activity.
Therefore, a need exists for a means for sustaining the release of biologically active hGH in vivo without causing an immune system response over the release period of the hGH.